(1) Field of the Invention
The present invention relates to a system and method for accurately detecting an intervehicle distance to a preceding vehicle moving on the same lane of a road as the vehicle in which the system is mounted in place.
(2) Description of the Prior Art
Systems for detecting an intervehicle distance from a vehicle in which a radar unit is mounted to a preceding vehicle present on the same traffic lane in front of the vehicle and controlling the vehicle speed to always follow the preceding vehicle at a predetermined safe intervehicle distance have conventionally been proposed. One of such conventional systems is exemplified by Japanese Patent Application Unexamined Open No. Sho. 55-86,000 published on June 28, 1980.
In the disclosed conventional system, the radar unit is used in which to measure the intervehicle distance an electromagnetic wave is transmitted toward a forward movement direction of the vehicle, a reflected electromagnetic wave is received from a reflecting object, the intervehicle distance to the preceding vehicle as the reflecting object is measured on the basis of a propagation delay time between times at which the transmission of the electromagnetic wave and reception of the reflected wave are carried out, and the measured intervehicle distance result is sent to a signal processing circuit. The signal processing circuit compares the measured intervehicle distance result with a safe intervehicle distance corresponding to a vehicle speed detected from a vehicle speed sensor and control an opening angle of a throttle valve installed in an engine of the vehicle via an actuator for independently actuating the throttle valve so as to maintain the distance to the preceding vehicle at the safe intervehicle distance. However, since an orientation of the electromagnetic wave transmitted from the radar unit in the above-described conventional system is in general limited within a narrow area in the forward direction of the vehicle, it is difficult to determine whether a wave reflecting object is really a preceding vehicle moving on the same lane or another forwarding vehicle moving on a different (adjacent) lane, e.g., when the vehicle is traveling on a curved road.
Therefore, the conventional system disclosed in the above identified document determines erroneously that the preceding vehicle moving on the adjacent lane is that moving on the same lane and accelerates or decelerates the vehicle inappropriately according to the erroneous intervehicle distance.
On the other hand, another similar system has been proposed in which, e.g., a laser beam transmitted from the radar is scanned within a predetermined range and a reflecting object of the laser beam within the predetermined range is detected.
This is exemplified by Japanese Patent Application Unexamined Open No. Sho. 58-96,267 published on June 8, 1983.
However, if such the conventional laser beam radar unit is applied to the previously described intervehicle distance controlling system, it is similarly difficult to determine whether the detected reflecting object is really a preceding vehicle moving on the same traffic lane. Consequently, the appropriate control of the vehicle speed cannot be achieved in the similar way.